I can't paint anymore! Beginner here
Unfortunately it's not possible to determine what's happening just from those screenshots, hence moonboots's comment requesting that you upload the broken file which demonstrates the strange behavior.
I've not seen a texture paint problem quite like this before. It may be caused by an unreported bug, perhaps due to some combination of your hardware and a new part of Blender's 2.80's viewport.

As it's unknown territory, the only advice available here will be either A) trying to diagnose what's really going on (i.e. asking many clarification questions); B) suggestions for working around it (eg as Craig D Jones suggests); or, C) if it's happening too consistently to ignore, you might consider submitting a bug report.

Before any of that: experimental builds of Blender are available to download, which are effectively daily updated '2.80+' with additional fixes and some newer features. You might want to try downloading the bleeding edge latest version, and see if the same problem still occurs in that.

Finally, if the problem is still happening, please consider using the Help > Report a Bug option. This option uploads operating system and graphics cards details which help pinpoint things with much less guesswork.
If you can find and describe the fewest steps to reproduce the error from a blank starting state, consistently (i.e. more than once) then that's invaluable for the devs to pinpoint it quickly if it is a new bug.
I know this doesn't help you immediately fix your problem today, but if this is something unreported, reporting it is the best way to get it resolved and then gone from the newest version.